Studies designed to identify the complementary structures on oral bacteria and mammalian cells which initiate attachment have demonstrated that adherence of Actinomyces naeslundii (WVU45) to several human epithelial cell lines is mediated by the lactose-sensitive fimbriae (type 2) of WVU45. This was determined by comparing the adherence of bacterial mutants which specifically lack the type 2 fimbriae and by using antibodies against the type 2 fimbriae which block attachment. The lectin-carbohydrate nature of the interaction was confirmed by specifically inhibiting attachment using Beta-galactosides and plant lectins which react with galactose or N-acetyl-galactosamine. These plant lectins which have specificities similar to that of the actinomyces fimbrial lectin are being used to identify the receptor on epithelial cells.